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Characterization of the Cu+ Sites in High-silica Zeolites Interacting with CO Molecule: Combined Computational and Experimental Study
Authors: Davidová Markéta | Nachtigallová Dana | Sobalík Zdeněk | Bulánek Roman | Nachtigall Petr
Year: 2003
Type of publication: ostatní - přednáška nebo poster
Name of source: 18th North American Catalysis Society Meeting
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cze xxx
eng Characterization of the Cu+ Sites in High-silica Zeolites Interacting with CO Molecule: Combined Computational and Experimental Study Characterization of the copper/zeolite systems attracts a large attention of both experimentalists and theoreticians. Knowledge about the details of the structure and coordination of copper ions in high-silica zeolites is essential for understanding the mechanism of deNOx processes at the atomic scale level. Often the CO molecule was used as a probe in characterization of the Cu+ sites in zeolites.(1-3) CO strongly interacts with Cu+ ions inside the zeolite matrix forming mono-, di-, and even tri-carbonyl species.(1) IR bands in the range 2129-2164 cm-1 (2157-2159 cm-1 for MFI) were assigned to CO stretching mode of mono-carbonyl. Some authors deconvoluted this band into two peaks (2151 and 2159 cm-1 for MFI) and assigned them to different Cu+ sites.(2) CO stretching band observed for Cu+/zeolite systems is blue-shifted with respect to the frequency of CO in the gas phase. The interaction of copper ions with MFI and FER frameworks was studied previously in our laboratory by means of the combined QM-pot technique.(4,5) Two dominant types of the Cu+ ion sites were identified in both zeolite frameworks. Sites where the Cu+ ions are coordinated to 3 or 4 oxygen atoms of six-membered ring on the wall of one of the channels are denoted ?type I? sites. Site where the Cu+ ions are coordinated to only two oxygen atoms of the AlO4 tetrahedron located on the channel intersection are denoted ?type II? sites. In this contribution we present the results of the combined quantum mechanical/interatomic potential function (QM-pot)(6) study of the CO interaction with copper sites in high-silica zeolites (MFI and FER) together with TPD and FTIR spectra of CO adsorbed in various high-silica zeolite matrices.The results of the combined QM-pot study show that two different Cu+ site types identified in high-silica zeolite matrices become very similar upon the interaction with the single molecule of carbon monoxide. The overall coordination number for Cu+ is 3 (2 framework oxygen atoms and Cu+ sites, zeolites, CO molecule

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